A plug-in hybrid electric vehicle (PHEV) provides the capability to operate significant distances solely in electric mode, without running the engine to recharge the battery. For example, some vehicle operators may exclusively take short trips, and may consistently plug in the vehicle between trips, such that the engine is infrequently started for charging.
Leone (US 2010/0300781) addresses degrading effects arising from long periods of engine inactivity, including water condensation, corrosion, stale fuel, and leakage of fluids past seals, or into the fuel system. To address these issues, Leone periodically starts and operates the engine, for example, to deplete stored fuel.
The inventor herein has recognized a potential issue with the above approach. Namely, while increased engine starting may address some issues, such as stale fuel, the increased number of starts, especially cold starts, can cause still other issues. For example, oil contamination may occur when the engine is inactive for extended periods of time, and can be exacerbated by increasing a number of cold engine starts. Specifically, when the engines are stopped and started repeatedly, especially when the engine is cold, gasoline and water contaminants can accumulate in the oil, thus degrading the oil and increasing friction and engine wear.
One approach that addresses the aforementioned issues is a method, comprising: propelling a vehicle with an engine and a motor; starting the engine if energy stored in an energy storage device is greater than an upper threshold level when a contaminant amount in engine oil is greater than a threshold. Further, such operation may occur even when the fuel in the fuel tank has recently been refilled. In this way, it is possible to harmonize fuel degradation along with oil degradation, while still providing efficient vehicle and engine operation.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.